1. Field of the Invention
This invention relates to a flat display device such as a liquid crystal display device, plasma display device, electronic emission type display device or a display device using organic EL and a control method thereof, and more particularly to a control method for gate signals output to scanning lines.
2. Description of the Related Art
Gate signals (which are also referred to as scanning signals) are supplied from a gate drive circuit to scanning lines of a liquid crystal display device. A gate inhibition circuit which inhibits gate signals from being unnecessarily output is provided in the gate drive circuit.
When the power supply of the device is turned ON, it takes a certain time until the operation of the display device is stabilized. During this time, if a gate signal is output to the scanning line of the display area, unnecessary light emission occurs in the display area and an unstable and disturbed state occurs on the screen. In order to prevent occurrence of such a phenomenon, conventionally, the gate signal is inhibited from being output for a preset period of time at the turn-ON time of the power supply (for example, Jpn. Pat. Appln. KOKAI Publication No. H11-119747).
However, the period in which the gate signal is unnecessarily output occurs at the time other than the turn-ON time of the power supply. For example, the period occurs at the input switching time or channel switching time. In such a case, a vertical sync. signal contained in the present video signal and a vertical sync. signal contained in a newly input video signal are asynchronous from each other. As a result, the gate signal is inadvertently output, which disturbs the image in some cases.
That is, gate signal output data which is transferred to a scanning line arranged in the intermediate position in the gate drive circuit (one of a plurality of scanning lines arranged in the vertical direction which is arranged in the intermediate position) is continuously transferred after channel switching or input switching and gate signals are sequentially output to the remaining scanning lines. At this time, since an input signal from the source drive circuit is not present, disturbance of the image appears on the screen.
Further, if the unnecessary gate signal is output, electric power is uselessly consumed. Therefore, outputting of the unnecessary gate signal is not preferable from the viewpoint of reducing the power consumption.